The invention is directed towards a pseudotetrahedral late transition metal catalyst complex and its use in forming xcex1-olefins.
The chemical industry uses xcex1-olefins as intermediates in a variety of processes. In particular, linear xcex1-olefins are used in the formation of polyolefins such as ethylene butylene copolymers. Other products formed from xcex1-olefins include surfactants, lubricants and plasticizers. Paraffin wax cracking, paraffin dehydrogenation and alcohol dehydration processes can be used to produce xcex1-olefins; however, most of the short chain linear xcex1-olefins currently used in the chemical industry are produced by ethylene oligomerization. Ethylene oligomerization is a desirable route due to the availability and low cost of ethylene. Additionally, the product quality is also acceptable for most applications.
In recent years, the chemical industry has employed the use of organometallic catalysts to produce polymers. While many advances in organometallic catalyst technology have been made, researchers continue to seek superior catalyst compositions. In fact, very recently, novel late transition organometallic catalysts have been discovered which are very effectively used in polymerization processes. More specifically, U.S. Pat. No. 6,037,297 to Stibrany et al., herein incorporated by reference, details group IB (Cu, Ag and Au) containing catalyst compositions that are useful in polymerization processes.
Organometallic catalyst technology is also a viable tool in oligomerization processes which produce linear xcex1-olefins for use as feedstock in various other processes. However, one problem often encountered when using many of these catalyst systems is the propensity to produce xcex1-olefins with very low selectivity (i.e., a Schulz-Flory type distribution with high k values). For instance, many of the linear xcex1-olefins made today utilize a neutral nickel (II) catalyst having a planar geometry and containing bidentate monoanionic ligands. While these planar nickel (II) catalysts do produce linear xcex1-olefins, these catalysis systems exhibit a Schulz-Flory type of distribution over a very wide range (i.e., C4-C30+).
To address Schulz-Flory distribution problem, chromium metal based catalysts have become popular for use in certain oligomerization processes. More precisely, chromium complexes have been used to oligomerize ethylene in order to form linear xcex1-olefins with improved distributions. In fact, there has been a report of a specific chromium catalyst which selectively trimerizes ethylene to 1-hexene. These techniques employ the use of a chromium compound in conjunction with aluminoxane along with one of a variety of compounds such as nitrites, amines and ethers. Unfortunately, while these techniques have been able to selectively produce xcex1-olefins, polymer is formed as a co-product. Of course, when polymer is co-produced, the yield of desirable product decreases accordingly. Also, as a practical matter, polymer build-up in the reaction vessel can severely hamper production efficiency thereby limiting the commercial use of such processes.
As discussed above, the organometallic catalyst technology now being used to produce xcex1-olefins has two major disadvantages. First, many of the organometallic catalysts produce xcex1-olefins with a Schulz-Flory type distribution. Unfortunately this Schulz-Flory type distribution is not ideal when short chain xcex1-olefins are desiredxe2x80x94in other words, the selectivity is not good enough to maintain efficient processes. Because xcex1-olefins are used as inter-mediates for specific products, xcex1-olefins with certain chain lengths are desired. For instance, the following are examples of xcex1-olefin chain lengths that would be desirable as feeds for certain product types: C4 to C8 for comonomer in ethylene polymerization; C10 for lube quality poly-xcex1-olefins; and C12 to C20 for surfactant products. Thus, considerable inefficiency and waste is present when significant amounts of xcex1-olefins produced having chain lengths outside of the range required for production of a particular chemical. Second, while some of the current organometallic catalysts may improve selectivity, most also produce polymer co-product. This lowers the yield of desired product and can also accumulate in the reaction vesselxe2x80x94both of which make commercial use less attractive and inefficient. Hence, there is still a need for improving the selectively and efficiency of linear xcex1-olefin production.
The instant invention provides a late transition metal catalyst composition having a pseudotetrahedral geometric structure and its use in forming xcex1-olefins. The instant invention can be used to selectively produce short chain xcex1-olefins without producing a significant percentage of polymer co-product. Thus, the two problems noted above with regard to current oligomerization processes are overcome.
In one embodiment, the invention is a composition having the formula LMX(Xxe2x80x2)n wherein n equals 0 or 1; X and Xxe2x80x2 are independently selected from the group consisting of halides, hydride, triflate, acetates, borates, C1 through C12 alkyl, C1 through C12 alkoxy, C3 through C12 cycloalkyl, C3 through C12 cycloalkoxy, aryl, thiolates, carbon monoxide, cyanate, olefins, and any other moiety into which a monomer can insert; M is selected from the group consisting of nickel, palladium, and platinum and L is a nitrogen-containing bidentate ligand with more than two nitrogen atoms.
In another embodiment, the invention is a catalyst composition comprising the reaction product of a composition having the formula LMX(Xxe2x80x2)n, as described above, and an activating cocatalyst. This embodiment of the invention is particularly useful in oligomerization chemistry.
Also provided for is a method for selectively and efficiently producing short chain linear xcex1-olefins. The method includes contacting olefinic monomers under oligomerization conditions with a catalyst composition comprising a composition having the formula LMX(Xxe2x80x2)n, as defined above, and an activating cocatalyst.
These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying FIGURE.